PROJECT ABSTRACT A strategy showing great promise for treating pancreatic cancer is to combine cytotoxic treatments with agents that abrogate the already-tenuous checkpoint functionality exhibited by most tumor cells. Drugs that target the checkpoint protein Chk1 (such as AZD7762, currently in Phase-I clinical trials) are of particular interest in the context of pancreatic cancer because Chk1 has also been shown to have a critical role in mediating the activity of Rad51, a key protein in homologous recombination repair (HRR) that is associated with resistance to DNA damaging treatments, and is upregulated in human pancreatic tumors. The long-term goal of our work is to improve the outcome of patients with pancreatic cancer by rationally adding Chk1 inhibitors to the combination of gemcitabine (Gem) + radiation. Our preliminary data show that AZD7762 is a potent chemo- and radiosensitizer of human pancreatic tumor cell lines that both decreases HRR and abrogates the G2/M checkpoint. Specific Aim 1 is to determine the relative roles of cell cycle checkpoint abrogation and HRR inhibition in chemo- and radiosensitization by AZD7762. This work will allow us to identify mechanism-based molecular endpoints to be interrogated in future clinical studies, and to identify new targets for therapeutic intervention related to HRR activity. We hypothesize that checkpoint abrogation and HRR inhibition each play key but differing roles in (to Gem) and by AZD7762. Our preliminary results using both established cell lines implanted as xenografts and early passage human tumor xenografts also show that AZD7762 is a potent chemo- and radiosensitizer in vivo, providing strong motivation for conducting a clinical trial. Specific Aim 2 is to use xenograft models to establish the basis for conducting a clinical trial combining AZD7762 with Gem + radiation, evaluating the role of drug schedule. The results of Aim 2 will help to define the design of our subsequent clinical trial. Specific Aim 3 is to carry out a clinical trial using AZD7762 in combination with Gem + radiation in patients with locally advanced, unresectable pancreatic cancer. We will use a combination of Gem + radiation followed by Gem alone, combined with dose-escalating AZD7762, based on the schedule suggested in Aim 2. We hypothesize that the MTD for AZD7762 will be similar to that determined in the current phase I trials using Gem alone (i.e. that adding conformal radiation will have a minimal impact on the MTD of AZD7762 in combination with Gem). Also, we hypothesize that AZD7762 will inhibit Chk1 activity in surrogate normal tissues when administered at the MTD, and, possibly, at lower doses.